The present invention relates to RTV compositions and more particularly, the present invention relates to the preparation and utilization of novel cross-linking agents and scavengers in the production of fast-curing, non-corrosive RTV compositions.
RTV silicone compositions are widespread and are utilized to produce sealants, molds for the production of molded parts, gasketing materials, etc. (RTV in this application refers to room temperature vulcanizable.) There are two types of RTV compositions: one is the one-component or one-package type; and the other is the two-component or two-package type. Examples of early one-component types are the ones, for instance, disclosed in Ceyzeriat U.S. Pat. No. 3,133,891 and Brunner U.S. Pat. No. 3,035,061. These patents disclose as the basic ingredients a silanol terminated diorganopolysiloxane polymer as the base polymer, an acyloxy functional silane as the cross-linking agent and a metal salt of a carboxylic acid as the condensation catalyst. As the Brunner patent notes there was formed in such compositions a diorganopolysiloxane polymer which had acyloxy functional terminal groups. Such composition was packaged in the substantial absence of moisture in a moisture proof package. When it was desired to use the composition, the seal on the package was broken and the composition was applied such that upon exposure to atmospheric moisture the acyloxy groups hydrolyzed to cross-link the polymer and form a silicone elastomer, with final cure taking place in anywhere from 24 to 72 hours. There was placed in the composition a metal salt of a carboxylic acid as a condensation catalyst. Preferably, such metal salt was a tin salt.
One disadvantage in such a composition is that it released acetic acid upon curing which was somewhat corrosive and gave off a somewhat unpleasant odor. There were various additives and other ingredients formulated into such compositions such as self-bonding additives and various other types of flame retardant additives. As time went on, various types of one-component RTV compositions were invented and produced, that is, compositions that were amine functional, that is the cross-linking agent was amine functional or ketoxime-functional or amide-functional, etc. However, there was a constant search to find a one-component RTV composition that is non-corrosive, that is, that the composition did not give off any corrosive by-products upon curing, and is fast curing.
It is important to note that there was also some development work in the two package or two-component area of RTV compositions. One, for instance, is disclosed in Nitzsche U.S. Pat. No. 3,127,363 which comprises mixing a polyalkoxysilane such as tetraethylsilicate or partial hydrolysis product thereof with the silanol end-stopped diorganopolysiloxane base polymer in the presence of a metal salt of a carboxylic acid. Although such composition was not corrosive and had fast-curing properties, nevertheless it did not have a sufficient shelf life after it was mixed. That is, the composition after it was mixed, had a short shelf life. It had to be used almost immediately. Accordingly, the composition could not be mixed and packaged as a single package and utilized as such. It had to be manufactured and sold in two components and then the worker in the field would mix the two components and apply them in accordance with the instructions. Not only were the instructions not always followed carefully in the preparation and application of such compositions, but also the labor involved increased the cost of utilizing such RTV compositions.
The disclosure of Nitzche et al U.S. Pat. No. 3,065,194 should be noted, in that this disclosure taught that a one-component RTV composition could be made from alkoxy end-block diorganopolysiloxane base polymer or an alkylortho silicate cross-linking agent and a tin soap as a curing catalyst. However, the disclosure noted that extreme drying procedures had to be carried out to see to it that a dry composition was prepared and that even with such a drying cycle in the preparation of the composition, the composition still had a relatively short shelf life. However, there were further formulations to make the two-component of Nitzsche et al one-component. Weyenberg U.S. Pat. No. 3,334,067, Cooper et al U.S. Pat. No. 3,542,901, Smith et al U.S. Pat. Nos. 3,689,454 and 3,779,986, disclose producing a one-component, non-corrosive, RTV silicone composition comprising a base silanol end-stopped polymer and an alkoxy cross-linking agent which preferably was methyltrimethoxysilane and condensation catalysts. These patents disclose the preferred type of condensation catalyst as various types of titanium chelate catalysts. The preferred condensation catalysts were titanium chelate catalysts such as that of Smith et al. U.S. Pat. Nos. 3,689,454 and 3,779,986 and to a lesser extent that of the Weyenberg patent which catalysts were effective in producing a low modulus, non-corrosive, one-component RTV composition which cured the composition completely but at a slow rate. However, the difficulty was that the tack-free time of such compositions was extended after storage for periods of time as small as five hours. Accordingly, such compositions were not fast curing, and various modifications had to be made such that they would cure at a sufficiently acceptable rate after being stored for periods of time of one year or more after manufacture. Such disclosures such as Weyenberg and Smith et al, went on the premise that the alkoxy-functional cross-linking agent was a desirable type of cross-linking agent in the production of a one-component system even though workers skilled in the art were not able to make an RTV composition that was sufficiently fast-curing and had shelf stability. Early work in this area of making such compositions shelf stable and having a sufficient cure rate as well as being non-corrosive is evidenced by the work disclosed in Brown et al U.S. Pat. No. 3,122,522 and Brown et al, U.S. Pat. No. 3,161,614 or U.S. Pat. No. Re. 29,760. In the latter patents Brown disclosed a polyalkoxy terminated diorganopolysiloxane polymer where this polymer was disclosed alone or in combination with a curing catalyst. However, even this polymer as disclosed in Brown et al, U.S. Pat. No. Re. 29,760 was not suitable as an RTV composition since it was not sufficiently fast-curing in the presence of most catalysts. It was with the development of the titanium chelate catalysts of Weyenberg, U.S. Pat. No. 3,334,067 and Smith et al, U.S. Pat. Nos. 3,689,454 and 3,779,986 that commercial one-component alkoxy-functional RTV systems were obtained. That is, systems that were non-corrosive. However, as was said before, these compositions would not cure at a sufficiently fast rate and did not have good shelf-stability.
Recently, there has been devised a suitable alkoxy-curing, non-corrosive one-component RTV system as disclosed in the patent application of White et al, entitled "One-Package Stable Moisture Curable Polyalkoxy-terminated Organopolysiloxane Compositions, A Method for Making," Ser. No. 277,524, filed on June 26, 1981, now U.S. Pat. No. 4,395,526. Another related disclosure is entitled, "Dialkoxysilanolethers and Method for Making,"--the invention of John E. Hallgren, filed on June 26, 1981, Ser. No. 277,525, now U.S. Pat. No. 4,377,706. The more important disclosure of White et al. discloses the production of non-corrosive, fast-curing one-component RTV compositions by utilizing a scavenger cross-linking agent to absorb and tie up the excess silanol in the polymer in the RTV composition mixture. It is theorized that in the past when alkoxy-functional cross-linking agents were incorporated along with silanol end-stopped polymers in the production of one-component RTV compositions, that even though the composition was dried prior to and after the incorporation of the alkoxy cross-linking agent, there was sufficient hydroxy species such as H.sub.2 O methanol present in the polymer mixture to de-stabilize and degrade the polymer mixture such that the desired alkoxy-terminated diorganopolysiloxane linear polymer was obtained in maximum yield. It has also been theorized that the methanol in the polymer attacks the alkoxy groups in the RTV mixture, and degrades such siloxane groups, thus lowering or decreasing the storage stability of the polymer mixture and resulting in the composition being slow curing. Irrespective of whichever of these theories are correct, it has been evidenced that methanol is undesirable in the RTV polymer mixture. It is desirable to have a scavenger in the system which will react with hydroxy groups to produce an unreactive compound which can stay as a filler in the RTV polymer mixture prior, during and after cure of the RTV composition. The functionality of the scavenger can be selected from an oximo, carbamato, enoxy, amino, amido, imidato, and ureido, isocyanato, and thioisocyanato. It should be noted that on page 21, RD-13,275 there is specifically disclosed under Amino Silanes, methyldimethoxy(caprolactamo)silane. However, this is the only cyclic amide that is disclosed in the application as a scavenger cross-linking agent for the non-corrosive RTV system of that application.
Accordingly, there is offered by the present disclosure additional cyclic amide functional scavengers that can be utilized in the production of one-component RTV non-corrosive, low Modulus, fast curing RTV compositions and the methods for preparing the same.
Accordingly, it is one object of the present invention to provide a process for producing a cyclic amide functional RTV scavenger and cross-linking agents.
It is an additional object of the present invention to provide novel cyclic amide functional cross-linking agents as scavenger compounds.
It is still an additional object of the present invention to provide for a one-component RTV system that is non-corrosive, fast curing and has shelf stability, and where the cross-linking agent is an alkoxy-functional silane having a cyclic amide functional scavenging group in the polymer mixture.
It is still an additional object of the present invention to provide for a process for forming a one-component RTV composition which is alkoxy-functional and which is fast-curing, low Modulus, non-corrosive, and shelf stable in which the excess silanol in the polymer is reacted with a cyclic amide functional scavenging agent.
It is still yet an additional object of the present invention to provide for a novel, one-component, non-corrosive fast curing, shelf stable RTV compositions in which the excess silanol in the RTV polymer mixture is reacted with a cyclic amide functional moiety present in the polymer mixture.
These and other objects of the present invention are accomplished by means of the disclosures set forth hereinbelow.